From: Eric Lemmons (ericlemmons@xxxxxxxxx)
Date: Sat Mar 30 2002 - 13:09:17 GMT-3
Regular expressions are very powerful.
You're not likely to encounter the "regular expression from hell", in
the lab.
The CCIE Powersession made this point at Networkers 2001. You should
be familiar with the basic regular expressions, $, _, and ^.
Regular expression writing can get to an almost "programming" level.
I've been amazed at what you can do with regular expressions in a
good editor.
Eric
--- "Williams, Glenn" <WILLIAMSG@PANASONIC.COM> wrote:
> FWIW, if perhaps on the lab they said use one statement to filter
> only AS
> 64118 to 64239 how would you do it? What I have played with that
> seems to
> work would be something like:
>
> ip as-path access-list 1 permit (64[1-2][1-3]9)
>
> If I don't have this just right, someone let me know.
> GW
>
>
> -----Original Message-----
> From: Michael C. Popovich
> To: D. J. Jones; Gregg Malcolm; ccielab@groupstudy.com
> Sent: 3/27/02 6:30 PM
> Subject: RE: BGP Reg Expressions
>
> I would agree with that statement.
>
> MP
>
> -----Original Message-----
> From: D. J. Jones [mailto:meganac@attbi.com]
> Sent: Wednesday, March 27, 2002 3:53 PM
> To: Gregg Malcolm; ccielab@groupstudy.com
> Subject: Re: BGP Reg Expressions
>
> Let me insert the whole command for completeness:
>
> ip as-path access-list 1 deny _150_
>
> dj
> ----- Original Message -----
> From: "Gregg Malcolm" <greggm@sbcglobal.net>
> To: <ccielab@groupstudy.com>
> Sent: Wednesday, March 27, 2002 1:01 PM
> Subject: Fw: BGP Reg Expressions
>
>
> > > Thanks Clay. Think the light is finally getting somewhat
> brighter
> for
> me.
> > > I set up a bunch of AS prepends on a router then played with
> filtering
> AS
> > > paths.
> > >
> > > From what I can see, there are a few important reg exp's to
> remember
> : _
> ^
> > > and $
> > >
> > > _ matches any instance. Good for filtering transit AS info.
> > > ^ matches the beginning. Used for filtering paths beginning
> with an
> AS
> > > number
> > > $ matches ends with. Used for filtering paths that end with an
> AS
> number.
> > > I find I must use _ then path then $ (eg _30$) to filter path
> that
> > > originated at path 30.
> > >
> > > I think these 3 along with .* and ^$ will hopefully get me
> thru the
> lab.
> > I
> > > believe that I can do any filtering with multiples of these.
> Let's
> say
> > that
> > > I was asked to deny all routes that originated in path 50 and
> all
> routes
> > > that passed thru 150 :
> > > ip as-path access-list 1 deny _50$
> > > ip as-path access-list 1 deny _150 (same as just 150 tho.. I
> need to
> test
> > > some more)
> > > ip as-path access-list 1 permit .*
> > >
> > > Sound right ? I'm certain that other expressions are very
> useful but
> I'm
> > not
> > > sure that I can remember them all. Plus, I'm not really sure
> that
> they
> > will
> > > be needed on the lab test.
> > >
> > > I've also found that sh ip bgp reg <expression> helps a bunch
> to
> test
> the
> > > expression before placing it in an as-path list. A great
> feature
> that I
> > > never really used before.
> > >
> > > Gregg
> > >
> > >
> > >
> > > ----- Original Message -----
> > > From: "Clay Maney" <clay@openworldinc.com>
> > > To: "Gregg Malcolm" <greggm@sbcglobal.net>
> > > Sent: Wednesday, March 27, 2002 11:09 AM
> > > Subject: Re: BGP Reg Expressions
> > >
> > >
> > > > I'm not the guru here by any measure, but I can tell you this
> for
> sure:
> > > >
> > > > the ^ means "beginning with" and the $ means "ending with".
> > > >
> > > > so, ^30 means "where 30 is the first AS in the list", etc.
> > > >
> > > > hope that helps (and please let me know if I'm wrong)
> > > >
> > > > Clay
> > > >
> > > > On Wed, Mar 27, 2002 at 10:44:35AM -0800, Gregg Malcolm
> wrote:
> > > > > Folks,
> > > > >
> > > > > Does anyone have any good tips to help to remember reg
> expressions ?
> > > > > Unfortunately, my Unix background is pretty weak. I can
> remember
> some
> > > of the
> > > > > simple stuff like .* is all paths, ^$ is local routes
> (empty),
> _30_
> is
> > > routes
> > > > > that passed thru path 30 , etc.
> > > > >
> > > > > The CD is very limited with info regarding this. Best CD
> info
> I've
> > > found is
> > > > > an appendix in the dial section :
> > > > >
> > >
> >
>
http://127.0.0.1:8080/cc/td/doc/product/software/ios121/121cgcr/dial_r/d
> rdap
> > > p
> > > > > /index.htm
> > > > >
> > > > > Mostly related to chat scripts from what I see. BTW - I
> swear
> that
> if
> > I
> > > see a
> > > > > chat script on the lab I'll get up and leave immediately.
> > > > >
> > > > > My confusion is not so much with the meaning of the
> expressions,
> but
> > > with how
> > > > > they are interpreted by BGP. For instance, what's the
> difference
> > > between ^30$
> > > > > and ^30_ ? Is it that ^30$ only matches 30 and nothing
> else and
> ^30_
> > > matches
> > > > > any path with 30 anywhere in it ?
> > > > >
> > > > > Does anyone have a standard set that they use that is
> somewhat
> easy
> to
> > > > > remember ?
> > > > >
> > > > > TIA, Gregg
> > > > >
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